The present invention generally relates to radio frequency circuitries that are implemented in radio devices, e.g. cellular telephones, and more particularly to an error detection circuitry for detecting an error on a transmission path between a radio system and a transmitter. The present invention is further related to a method for detecting an error on a transmission path between a radio system and a transmitter.
In special types of radio devices, the transmitting system is not directly attached to the radio device. For example, in mobile stations implemented in a railway train, a radio frequency (RF) cable provides a connection between the radio itself (located inside the driver cabin) and the antenna (located outside). It is desirable to check the quality of the RF connection and to detect a damaged, missing or obstructed antenna, e.g. during system start-up or at any desired time. A monitoring of the RF connection might be necessary due to safety purposes.
U.S. Pat. No. 5,287,555 discloses a method for checking a RF connection and an antenna. A directional coupler is provided as a part of the transmitter circuitry in order to determine the power that is reflected from the transmitting system. It is determined, whether such xe2x80x9creversexe2x80x9d power is within a normal range. A reverse power within the normal range indicates a proper performance of the transmitting system.
However, if there is no access to internal signals of the transmitter system available, e.g. in the case that the transmitter system belongs to a third party supplier and the antenna is not directly attached to the radio, the above mentioned method has a drawback. If there is no access to the transmitter system, the decision between normal operation and an error case only on the basis of the amplitude of a reflected signal is not sufficient. The reason for this is that in real systems a certain RF power reflection always occurs; thus, in the case that the transmitter system operates in a wide range of output power, it is very difficult or even impossible to define an appropriate reference level in order to distinguish between normal operation and an error.
A further problem that is related to the separation between the radio and the transmitter system occurs in digital systems that operate in a TDMA mode (xe2x80x9cTime Divisional Multiple Accessxe2x80x9d). Since the RF signals in a TDMA radio communication system are intermittent, a sampling of the signals must take place at an appropriate time. Thus, a timing is required that synchronizes the sampling and the occurrence of the reverse signal. In systems with access to the transmitter system a general timing signal may be used in order to define the timeslots and further for timing of the sampling. Such timing signal can advantageously be provided by a microprocessor. However, in a system without access to the transmitter system, there is also no access to a separate timer of the transmitter system. Thus, a general timing signal for the transmitter system and for the radio is not available.
Due to the possible separation between the transceiver system and the radio there are more difficulties related to the sampling of TDMA signals. In particular, a further problem arises with the introduction of the GPRS (xe2x80x9cGeneral Packet Radio Servicesxe2x80x9d) protocol since the GPRS protocol is not restricted to use a single timeslot within a frame, but more than one timeslot may be occupied depending on the communication requirements.
These and other problems related to the prior art systems will be discussed further below with reference to the accompanying drawings.
The present invention seeks to solve the above mentioned problems and to provide an error detection circuitry and a method for detecting an error that are applicable to a system in which a transmitting system is not directly attached to a radio.